U.S. Pat. No. 3,554,237 discloses wire-reinforced flexible duct requiring an adhesive and or tape along the internal wall and along the external wall for retaining the wire reinforcement. The present invention employs ultrasonic welding in the fabrication process which welds the inner strip to the outer strip enveloping and retaining the helical wire reinforcement under compression to produce a strong semi rigid and fully extended duct that does not sag, and may be shipped in a collapsed state. The present invention eliminates the need for a separate adhesive means and extra fabrication equipment normally required to apply the adhesive means to the duct construction which produces a limpid duct which is costly to install and offers greater air resistance.